1. Field of the Invention
The present invention relates to a wideband omnidirectional antenna, and more particularly, to a wideband omnidirectional antenna for a plug and play device.
2. Description of the Prior Art
With a rapid growth of demands for short-distance wireless transmission, massive provision of wireless local area network and diversification of personal mobile communication products, data throughput and transmission rate of wireless communication have been simultaneously increasing. Whereas this, the US Federal Communications Commission (FCC) authorizes ultra-wideband (UWB) transmission technology eligible for commercial communications system in February 2002. The ultra-wideband transmission technology is developed as a high transmission rate (data rate over 100 Mbs), low power (less than −41 dBm/MHz), and short-distance (effective radius smaller than 10 meters) communications system extremely suitable for transmitting multimedia video data of 400 Mbs, which allows wirelessly sharing DVD-quality recorded programs in home environment. In addition, the Institute of Electrical and Electronics Engineers (IEEE) develops a standard of wireless personal area network, IEEE 802.15.3 WPAN, including advantages of high transmission rate and low power for satisfying mobile communications consumer products having high definition (HD) applications.
Among architecture of the prior art wideband antennas, a metal planar antenna has most practical value. In general, the metal planar antenna has a larger size and is installed above the center of a large metal ground plane, suitable for the use of a wideband access-point antenna. US patent, publication No. 20050062670, discloses various types of planar wideband antennas applied to wideband communications (3.1-10.6 GHz). However, in practice, the sizes of the antennas are too large to be installed on a wireless plug and play device, such as universal serial bus (USB) devices. In addition, the planar wideband antennas have shortcomings of instability with respect to radiation patterns, where omnidirectional properties become worse as operating frequencies increase. In order to improve such problem, US patent, publication No. 20050243009, discloses an omnidirectional broadband monopole antenna, which bends a metal plate several times for controlling radiation patterns of two horizontal directions, so as to satisfy requirements of a wideband omnidirectional antenna. However, such omnidirectional broadband monopole antenna is also installed above the center of a large metal ground plane, which is not suitable for the plug and play devices.
Therefore, how to design an antenna, suitable for wireless plug and play devices and wideband applications, satisfying requirements of omnidirectional radiation patterns, and having simple, easy, and small-sized architecture, is a major objective for those skilled in the art.